This study will gather further knowledge concerning the specific antigenic composition of Treponema pallidum; it will also determine the type and magnitude of host responses to various individual treponemal antigens. Immunochemical studies of T. pallidum from syphilitic lesions in rabbits will yield the antigenic reagents. Both humoral and cellular responses to these antigens will be measured during the course of syphilis infection. These will be correlated with the clinical manifestations of disease and with the development or resistance to super-infection and/or re-infection. In this manner we hope to elucidate the role of host immune responses in the pathogenesis of disease; and in protection against infection. In our opinion such knowledge represents an essential prerequisite for the development of biologic measures for the prevention of human disease.